1. Field of the Invention
This invention relates to a heating collar for heating a pipe or the like by induction heating; more particularly this invention relates to a heating collar having four separate, but cooperating, coils or windings.
2. Background of the Invention
In many processes, in the fabrication and construction of pipes or pipelines, or in the application of coating and the like to such pipes, it is frequently desirable to preheat the pipe in the predetermined area or zone to be treated such as in welding, pipe coating and similar processes. Such zonal heating has been effected in the past, for example, by applying a torch flame to the area to produce the desired heat. However, the heating effects produced by a torch flame are highly localized, and are not suitable for many processes which require a uniform heat application, for instance, around the circumference of the pipe.
For example, in field performed processes in which a coating of epoxy or the like is sprayed onto a previously welded pipe joint, the entire area of the joint to be coated should be uniformly and evenly preheated to a temperature of 300.degree.-500.degree. F. prior to the application of he coating material to enable a desired uniform epoxy coat of, for instance, 25-35 mils to be deposited. Such coating processes are used, for instance, in applications in which pipes are provided with a protective epoxy coat, except for its ends at which welding to adjacent pipe sections in the field is effected. After the welding process, the uncoated joint is coated with epoxy to thereby effect a pipe coated along the entire length of the pipe, including the welded junction, for resisting corrosion and other deleterious influences to which the pipe may be subjected. Uneven heat, such as by torch preheating, may produce uneven or unreliable coatings, which may result in areas of the pipe being undesirably exposed to the elements, resulting in premature pipeline failures. The torch preheating also is slow to perform, usually done manually, and requires carrying the torch and its accessories from each joint to the next.